Anticausal system and Acausal system

• An anticausal system is a hypothetical system with outputs and internal states that depend solely on future input values. Some textbooks and published research literature might define an anticausal system to be one that does not depend on past input values (i.e. its outputs and internal states depend only on future and possibly present input values).
  
• An acausal system is a system that is not a causal system, that is one that depends on some future input values and possibly on some input values from the past or present. This is in contrast to a causal system which depends only on current and/or past input values. This is often a topic of control theory and digital signal processing (DSP).

Anticausal systems are also acausal, but the converse is not always true. An acausal system that has any dependence on past input values is not anticausal. ... (continued on: Wikipedia: Anticausal system)